Timaru's air pollution woes could be stopping people being more active during the day, and causing more hospital admissions.

A recent World Health Organisation report showed Timaru having the highest average level of particulate pollution in New Zealand, nearly twice as high as Auckland.

Air quality scientist Dr Gerda Kuschel said there had not been any significant reduction in the annual average in recent years.

"The number of high pollution nights is decreasing, but the overall average has not decreased by much. With the district's population increase in the last few years, I don't see the problem going away any time soon."

Kuschel was the co-author of the "Health and Air Pollution in New Zealand" report, jointly funded by the Health and Environment Ministry.

According to the report's latest estimates - based on the most recent census results, and the average particulate pollution rate - the town recorded more than 34,000 "restricted activity days".

Kuschel said restricted activity days could be anything from time off work or visiting the GP.

"In other words, the average Timaruvian would lose at least one or two days a year. It's those days when you are too wheezy or too sick to do what you should be doing. It's calculated on the amount of particulate pollution, and people's exposure to it.

"Older people and young people are really the ones who feel it the worst," Kuschel said.

Timaru GP Dr Bruce Small said the town's smog problem has been ongoing.

"I deal with a small number of patients who have issues with respiratory conditions made worse by the smog . . . this is a long-standing problem which is discussed each year with little forward progress."

Small believes a reduction in smoky fires and chimneys is the answer. In the last year, Environment Canterbury has received 107 separate complaints about smoky chimneys in Timaru, but so far, there have been no prosecutions.

Timaru Hospital recorded more than 400 separate discharges for respiratory illnesses per year.

However, South Canterbury District Health Board acting chief executive Fiona Pimm said it would be overstating the case to make a direct correlation between those discharges and the town's air quality.

In the past decade, Timaru has recorded 30 to 50 high pollution nights a year. By 2016, it is allowed to record only three, or face possible restrictions to development.